The objective of this project is the development of a generator system to produce an ultrashort-lived radionuclide generator for clinical and investigative work in the cardiovascular system; namely, radionuclide angiocardiography. A disadvantage with presently available radionuclides is their relatively long physical half-life which precludes the obtention of more than one projection each time, and to study the effects of exercise and pharmaceuticals in the hemodynamics. Once the study is completed, the patient continues to receive irradiation unnecessarily. We are considering a generator system to produce Se77m (Br77 yields Se77m). Se77m has a physical half-life of 18.1 sec and decays by isomeric transition with emission of approximately 162 KeV photons in approximately 50% abundance. The generator system will be made sterile and free of pyrogens. The radiochemistry and the animal work will be performed with longer-lived radionuclides of the daughter product. Biological distribution, kinetic and toxicity studies will be carried out in various animal species including primates. Animal studies using the gamma camera and the computer will be performed and computer programs for decay correction will be developed. If the generator is successfully developed, we will consider the use of Selenium-77m in humans, following application and approval by the Clinical Investigation Committee of the CHMC. This radionuclide would be useful in the clinic for cardiovascular studies (i.e., detection, localization and quantitation of intracardiac shunts, ejection fraction and qualitative radionuclide angiocardiography. This ultrashort-lived radionuclide will allow: a) greater amounts of information because multiple projections of the flow through the central circulation will be possible; b) evaluation of the degree of shunting and other physiologic parameters during rest and exercise or under the effect of certain drugs; and c) significant reduction of the radiation dose to patients, compared to the presently available radionuclides.